Method of selective dormant data session reactivation

ABSTRACT

A method of selective dormant data session reactivation in a radio access network includes calculating an activation rate threshold as a function of a first plurality of packets received over a first time interval, where the first plurality of packets are coupled to reactivate at least one dormant mobile station. The second plurality of packets received in a second time interval are buffered, where each of the second plurality of packets has a destination IP address to reactivate the at least one dormant mobile station. An arrival rate of the second plurality of packets in the second time interval is compared to the activation rate threshold. If the arrival rate exceeds the activation rate threshold, the second plurality of packets may be separated into a plurality of source IP groups according to their respective source IP addresses, and progressively discarding in descending order one of the plurality of source IP groups having a highest number of the second plurality of packets until the arrival rate is below the activation rate threshold.

BACKGROUND OF INVENTION

In cellular network systems, particularly CDMA cellular networks, amobile station may be in a dormant state, where the cellular network isaware of the mobile station on the system, but currently, there is noactivity with the mobile station. In other words, the mobile station isregistered with the cellular network, but is in a dormant data sessionas no active communication sessions are taking place. An example of thisis a mobile station that is registered and has been active in thecellular network, but is currently inactive without having powered off,such as a mobile station in a push-to-talk session, a mobile stationawaiting a paging request, and the like.

In prior art CDMA cellular networks, Internet users may cause abnormallyhigh paging rates by implementing malicious Internet Protocol (IP) scansof IP addresses terminated on such dormant mobile stations. Such IPscans can overload the cellular network system. These malicious IP scansmay or may not be intentionally implemented to search for mobilestations in a dormant data session in order to reactivate them. However,whether intentional or not, IP scans of mobile stations in a dormantstate does load a cellular network with mobile page attempts. The priorart is deficient in distinguishing these malicious users of the cellularnetwork system from legitimate users.

There is a need, not met in the prior art, for a method of selectivedormant data session reactivation. Accordingly, there is a significantneed for an apparatus and method that overcomes the deficiencies of theprior art outlined above.

SUMMARY OF THE INVENTION

To overcome the deficiencies described above, a method of selectivedormant data session reactivation in a radio access network isdisclosed. The method includes calculating an activation rate thresholdas a function of a first plurality of packets received by a packetcontrol function operating in a radio access network over a first timeinterval. The first plurality of packets is coupled to reactivate atleast one dormant mobile station operating in a wireless communicationsystem. The method also includes buffering a second plurality of packetsreceived in a second time interval, wherein each of the second pluralityof packets has a destination IP address coupled to reactivate thedormant mobile station. The method compares an arrival rate of thesecond plurality of packets in the second time interval to theactivation rate threshold. If the arrival rate exceeds the activationrate threshold, the second plurality of packets are separated into aplurality of source IP groups according to their respective source IPaddresses and one of the plurality of source IP groups having a highestnumber of the second plurality of packets is discarded. Until thearrival rate is below the activation threshold, the method includesiteratively comparing the arrival rate of the second plurality ofpackets in the second time interval without the one of the plurality ofsource IP groups, to the activation rate threshold and if the arrivalrate of the second plurality of packets in the second time intervalwithout the one of the plurality of source IP groups exceeds theactivation rate threshold, discarding the one of the plurality of sourceIP groups having a next highest number of the second plurality ofpackets.

BRIEF DESCRIPTION OF THE DRAWINGS

Representative elements, operational features, applications and/oradvantages of the present invention reside inter alia in the details ofconstruction and operation as more fully hereafter depicted, describedand claimed—reference being made to the accompanying drawings forming apart hereof, wherein like numerals refer to like parts throughout. Otherelements, operational features, applications and/or advantages willbecome apparent in light of certain exemplary embodiments recited in theDetailed Description, wherein:

FIG. 1 representatively illustrates a block diagram of a wirelesscommunication system in accordance with an exemplary embodiment of thepresent invention;

FIG. 2 representatively illustrates a more detailed block diagram of awireless communication system in accordance with an exemplary embodimentof the present invention; and

FIG. 3 representatively illustrates flow diagram in accordance with anexemplary embodiment of the present invention.

Elements in the Figures are illustrated for simplicity and clarity andhave not necessarily been drawn to scale. For example, the dimensions ofsome of the elements in the Figures may be exaggerated relative to otherelements to help improve understanding of various embodiments of thepresent invention. Furthermore, the terms “first”, “second”, and thelike herein, if any, are used inter alia for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order. Moreover, the terms “front”, “back”, “top”,“bottom”, “over”, “under”, and the like in the Description and/or in theClaims, if any, are generally employed for descriptive purposes and notnecessarily for comprehensively describing exclusive relative position.Any of the preceding terms so used may be interchanged under appropriatecircumstances such that various embodiments of the invention describedherein may be capable of operation in other configurations and/ororientations than those explicitly illustrated or otherwise described.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following representative descriptions of the present inventiongenerally relate to exemplary embodiments and the inventor's conceptionof the best mode, and are not intended to limit the applicability orconfiguration of the invention in any way. Rather, the followingdescription is intended to provide convenient illustrations forimplementing various embodiments of the invention. As will becomeapparent, changes may be made in the function and/or arrangement of anyof the elements described in the disclosed exemplary embodiments withoutdeparting from the spirit and scope of the invention.

Software blocks that perform embodiments of the present invention can bepart of computer program modules comprising computer instructions, suchcontrol algorithms that are stored in a computer-readable medium such asmemory. Computer instructions can instruct processors to perform anymethods described below. In other embodiments, additional modules couldbe provided as needed.

A detailed description of an exemplary application, namely a method ofselective dormant data session reactivation, is provided as a specificenabling disclosure that may be generalized to any application of thedisclosed system, device and method in accordance with variousembodiments of the present invention.

Wireless communication systems are well known and consist of many typesincluding land mobile radio, cellular radiotelephone (inclusive ofanalog cellular, digital cellular, personal communication systems (PCS)and wideband digital cellular systems), and other communication systemtypes. In cellular radiotelephone communication systems, for example, anumber of communication cells are typically comprised of one or moreBase Transceiver Stations (BTS's) coupled to one or more Base StationControllers (BSCs) or Central Base Station Controllers (CBSCs) andforming a Radio Access Network (RAN). The BSCs or CBSCs are, in turn,coupled to a Mobile Switching Center (MSC) that provides a connectionbetween the RAN and an external network, such as a Public SwitchedTelephone Network (PSTN), as well as interconnection to other RANs. EachBTS provides communication services to a mobile station (MS) located ina coverage area serviced by the BTS via a communication resource thatincludes a forward link for transmitting signals to, and a reverse linkfor receiving signals from, the MS.

FIG. 1 representatively illustrates a block diagram of a wirelesscommunication system 100 in accordance with an exemplary embodiment ofthe present invention. Wireless communication system 100 includes a RAN104 comprising multiple BTSs 106-108 that are each coupled to a CBSC110. RAN 104 is coupled to an MSC 114, and MSC 114 is in turn coupled toan external network 116 and provides a communication link between theexternal network, or other RANs, and RAN 104. In an embodiment, RAN 104is a CDMA network.

Wireless communication system 100 further includes a mobile station 102,103, 105 that may be in a dormant data session with a BTS 106, 107, 108.That is, mobile station 102 if it is in a dormant data session, forexample, is not in an active communication session with BTS 106, but ispowered-up, registered and may have been recently in an activecommunication session with BTS 106. While RAN 104 is aware of mobilestation 102, no active communication is currently occurring betweenmobile station 102 and RAN 104. In a dormant data session, mobilestation 102 is a dormant mobile station, which is registered with RAN104 and coupled to send or receive data via wireless link 120. Eachcommunication link 120, 130, 140 includes a respective forward link forconveyance of signals to mobile station 102 and a respective reverselink for receipt of signals from the mobile station 102. Either mobilestation 102 receiving a data packet via RAN 104, or a user of mobilestation 102 sending a data packet may reactivate dormant data session.Any number of mobile stations 102, 103, 105 may be coupled to RAN 104and be in a dormant data session.

CBSC 110 may also include Packet Control Function (PCF) 118. In anembodiment, PCF 118 is coupled to communicate packet data, particularlyIP packet data, between the mobile station 102, and the Packet DataServing Node (PDSN) 139 over an interface, the A10/A11 interface in thecase of a CDMA network. Packet control function 118 may operate tomaintain a reachable state between RAN 104 and mobile station 102,ensuring a consistent link for data packets, buffering of data packetsarriving from PDSN 139 when wireless link resources are not in place orare insufficient to support the flow from PDSN 139, and relay datapackets between the mobile station 102 and PDSN 139. PCF 118 is notlimited to a PCF in a CDMA network and may include one or more nodes inother radio access networks such as GSM, TDMA, and the like, thatperform a substantially similar function.

PDSN 139 may be coupled to operate as the gateway from the RAN 104 intoa public and/or private packet network, for example and withoutlimitation, the Internet 113. In an embodiment, PDSN 139 may act as anetwork access server, home agent, foreign agent, and the like. PDSN 139may manage the radio-packet interface between RAN 104 and Internet 113,provide IP addresses for the subscriber's mobile station 102, 103, 105,perform packet routing, actively manage subscriber services based onprofile information, authenticate users, and the like.

In an embodiment, PCF 118 may be coupled to receive incoming datapackets addressed to a dormant mobile station 102. In other words, PCF118 may be coupled to receive incoming data packets addressed toreactivate a dormant data session with mobile station 102. Such incomingdata packets may originate from a packet data network external to RAN104, such as users connected to the Internet 113, and the like. As anexample, incoming data packets may be incoming data coupled with apush-to-talk session, paging request, and the like. For example, mobilestation 102 may be registered with RAN 104 but have no currently activedata sessions in progress, i.e. mobile station 102 is in a dormant datasession. The arrival of a data packet, for example as part of a pagingrequest, may operate to reactivate dormant data session by reactivatingdormant mobile station 102.

In an embodiment, PCF 118 is coupled to examine incoming data packetsand determine if reactivation of a dormant data session with a dormantmobile station is permitted. In an exemplary embodiment, PCF may scanincoming data packets, including source IP addresses and destination IPaddresses to determine if an incoming data packet is the product of amalicious IP scan or from a legitimate user.

In an illustrative embodiment, a plurality of packets 160 may bereceived by PCF 118 via PDSN 139. In an embodiment, plurality of packets160 may include any number of data packets, for example and withoutlimitation IP packets. Each of plurality of packets 160 may have asource IP address 142 and a destination IP address 141. The source IPaddress 142 is an indication of the origination of the data packet,while the destination IP address 141 may be coupled to reactivate one ormore dormant mobile stations 102, 103, 105. In other words, one or moreof plurality of packets 160 may be addressed to reactivate a dormantdata session with one or more of dormant mobile stations 102, 103, 105.This can be, for example, a paging request, and the like.

FIG. 2 representatively illustrates a more detailed block diagram of awireless communication system 200 in accordance with an exemplaryembodiment of the present invention. Only one BTS 107 and one mobilestation 103 are shown for clarity. However, other BTS's and mobilestations may be included and be within the scope of the invention.

As shown in FIG. 2, the plurality of packets 160 arriving at the RAN maybe processed by the PCF 118. In an embodiment, plurality of packets 160may include any number of data packets, for example, IP packets. In anembodiment, the PCF 118 creates a sliding window average over a timeinterval of plurality of packets arriving that request the reactivationof a dormant data session of a dormant mobile station 103. Based on thisaverage, a dynamic threshold may be created such that any single timeinterval in which the arrival rate of packets requesting reactivationexceed the dynamic threshold, the PCF may discard a number of packetsfrom one or more source IP addresses such that the arrival rate fallsbelow the dynamic threshold.

In an embodiment, incoming packets may be buffered such that PCF 118examines incoming plurality of packets over a previous time interval todetermine what packets to discard during the current time interval.During normal operation of RAN 104, the reactivation rate of dormantmobile stations (number of reactivations per unit time) remains fairlyconstant when averaged over a short period of time. A surge inreactivation rates may be detected when the variance in reactivationrate relative to a short term average exceeds a predefined limit. At theonset and for the duration of a surge, the source address of those datapackets associated with reactivation requests may be analyzed todetermine the total number of reactivation requests per unit timeassociated with each source IP address.

In an embodiment, to determine if a surge condition exists, the arrivalrate of packets requesting reactivation can be compared with a multipleof the short term average of reactivation requests from a previous timeinterval. For example and without limitation, if the reactivation rateover a five second time interval is ten reactivations per second, then asurge in reactivation requests may be defined as a multiple of thisnumber, say five to six times, or fifty to sixty reactivations in a onesecond time interval.

If a surge condition is detected, PCF 118 may examine packets requestingreactivation and identify the source address(es) most responsible forthe surge condition and discard those packets such that they are neverprocessed and do not reactivate a dormant mobile station. For example,packets may be sorted into groups from high number of packets to lownumber of packets based on their source IP address. The group of packetsfrom a single source IP address with the highest number of packets maybe discarded and the algorithm re-run if necessary to discard the groupof packets with the next highest number of packets based on source IPaddress. This may continue until enough packets are discarded toalleviate the surge condition. The packets that are not discarded may beprocessed as normal and reactivate a dormant mobile station.

As shown in FIG. 2, PCF 118 may receive a first plurality of packets 150over a first time interval 151. First time interval 151 may be selectedto suit a given application. For example and without limitation, firsttime interval 151 may be approximately five seconds. First plurality ofpackets 150 may be data packets that are coupled to request areactivation of a dormant mobile station 103. Based on the number offirst plurality of packets 150 requesting reactivation received in firsttime interval 151, an average number of reactivation requests receivedin a given time interval, for example one second, may be calculated.From this, activation rate threshold 149 may be calculated. In anembodiment, activation rate threshold 149 may be a multiple of theaverage of the arrival rate of first plurality of packets (firstplurality of packets 150 received over first time interval 151). Inother words, activation rate threshold 149 may be a multiple of theaverage number of reactivation requests received in a given timeinterval. The multiple number (multiplier) may be chosen such thatactivation rate threshold 149 represents the point at which a surgecondition is imminent. In other words, the average arrival rate may becalculated over first time interval 151 and this average arrival rate ina given time period may be multiplied by a multiplier to yieldactivation rate threshold 149. For example, if the average arrival rateover the first time interval 151 is ten reactivation requests per secondover a five second time interval (first time interval 151), thenactivation rate threshold may be a multiple of the ten reactivationrequests per second as described above.

In an embodiment, PCF 118 may buffer and store a second plurality ofpackets 152 received in a second time interval 153 where each of secondplurality of packets 152 has a destination IP address 141 coupled toreactivate at least one dormant mobile station 103. Second time interval153 may be selected to suit a given application. For example and withoutlimitation, second time interval 153 may be approximately one second. Inan embodiment, second time interval 153 follows first time interval 151as shown in FIG. 2. Also, first time interval 151 may be longer thansecond time interval 153 so as to maintain an adequate sample ofreactivation requests for calculating activation rate threshold 149. Inanother embodiment not shown in FIG. 2, second time interval 153 may bea portion of first time interval 151.

In an embodiment, an arrival rate 143 of second plurality of packets 152may be calculated. This may be the number of second plurality of packets152 arriving in second time interval 153. The arrival rate 143 of thesecond plurality of packets 152 may then be compared to the activationrate threshold 149 calculated above. If the arrival rate 143 exceeds theactivation rate threshold 149, then the second plurality of packets 152may be separated into a plurality of source IP groups 145 according totheir respective source IP addresses. For example, the portion of secondplurality of packets 152 having the most number of packets from onesource IP address may be grouped into a source IP group having thehighest number 170 of second plurality of packets. The portion of secondplurality of packets 152 having next highest number of packets fromanother source IP address may be grouped into a source IP group having anext highest number 171 of second plurality of packets, and so on fornext highest numbers 172, 173. Any number of groups of second pluralityof packets may be created for plurality of source IP groups 145.Further, any number of a portion of second plurality of packets may beincluded in each of source IP groups 145. In an embodiment, if thearrival rate 143 of second plurality of packets 152 is less than theactivation rate threshold 149, then the second plurality of packets 152may proceed to be processed by PCF and reactivate one or more dormantmobile stations 103.

In an embodiment, a selective reactivation algorithm 147 mayprogressively discard in descending order, one of the plurality ofsource IP groups 145 having a highest number of second plurality ofpackets until the arrival rate 143 is below the activation ratethreshold 149. In an embodiment, progressively discarding in descendingorder may include discarding one or more source IP groups having thehighest number 170 of second plurality of packets 152 all at once. Inthis embodiment, selective reactivation algorithm 147 may evaluate whichof the plurality of source IP groups 145 should be discarded to bringthe arrival rate 143 below the activation rate threshold 149 and thendiscard the one or more plurality of source IP groups all at once.

In another embodiment, progressively discarding in descending order mayinclude discarding the source IP group having the highest number 170 ofsecond plurality of packets 152 and then comparing the arrival rate 143of the second plurality of packets 152 in the second time interval 153without the discarded source IP group, to the activation rate threshold149. If the arrival rate of the second plurality of packets 152 in thesecond time interval 153 without the discarded source IP group stillexceeds the activation rate threshold 149, the source IP group havingthe next highest number 171 of second plurality of packets 152 may bediscarded. Comparing and discarding source IP groups in descending orderbased on number of second plurality of packets 152 in the source IPgroup may iteratively continue until the arrival rate 143 falls belowthe activation rate threshold 149.

In an embodiment, during a third time interval 155, any of secondplurality of packets 152 not discarded may be processed and allowed toreactivate one or more dormant mobile stations 103. In effect,discarding any of the second plurality of packets 152 in one or more ofthe source IP groups 145 has the effect of preventing the discardedpackets from being processed and reactivating a dormant mobile station103.

In an embodiment, a protected sender may be defined such that anypackets from the protected sender may be allowed to pass through and beprocessed by the PCF 118 to allow reactivation of a dormant mobilestation 103. A packet from a source IP address of a protected sender maybe prevented from being separated into one of the plurality of source IPgroups 145 and subsequently discarded. This allows packets from one ormore protected senders to not be classified as malicious packets andactivate one or more dormant mobile stations 103.

In an embodiment, first time interval 151, which is used to calculateactivation rate threshold 149 is a sliding window average over a timeinterval of plurality of packets arriving that request the reactivationof a dormant data session of a dormant mobile station 103. In otherwords, first time interval is not fixed, but continues to update withthe most current data. This allows for updating the average number ofreactivation requests received over first time interval 151. This allowsfor activation rate threshold 149 to be dynamic and change with time. Adynamic activation rate threshold 149 prevents the erroneous discardingof reactivation requests that may otherwise be legitimate as the averagenumber of reactivation requests can change over time.

FIG. 3 representatively illustrates flow diagram 300 in accordance withan exemplary embodiment of the present invention. In this embodiment,the flow is invoked for each time step. In step 302, the PCF calculatesthe activation rate threshold as a function of first plurality ofpackets received over a first time interval, where the first pluralityof packets are coupled to reactivate at least one dormant mobilestation.

In step 304, a second plurality of packets received over a second timeinterval are buffered, where each of the second plurality of packets hasa destination IP address coupled to reactivate at least one dormantmobile station. In step 306, the arrival rate of the second plurality ofpackets in the second time interval is compared to the activation ratethreshold. In step 308, it is determined if the arrival rate exceeds theactivation rate threshold. If the arrival rate in step 308 does notexceed the activation rate threshold, then in step 309 all of the secondplurality of packets may be processed without discard and allowed toreactivate one or more mobile devices in a dormant state. The processthen adjusts to the next time step in step 320.

If the arrival rate exceeds the activation rate threshold in step 308,then in step 310 the second plurality of packets are separated into aplurality of source IP groups based on their respective source IPaddress. The process then begins progressively discarding in descendingorder one of the plurality of source IP groups having a highest numberof second plurality of packets until the arrival rate is below theactivation rate threshold. In step 312, the source IP group having thehighest number of second plurality of packets is discarded.Subsequently, in step 314, it is determined if the arrival rate of thesecond plurality of packets in the second time interval without thediscarded IP source group (highest, next highest, and the like) is abovethe activation rate threshold. If not, then the second plurality ofpackets that are not discarded are processed and allowed to reactivateone or more dormant mobile stations per step 318.

If the arrival rate is still greater than the activation rate thresholdin step 314, then the source IP group having the next highest number ofsecond plurality of packets is discarded per step 316. Steps 314 and 316may iteratively repeat themselves, discarding the source IP group havingthe next highest number of second plurality of packets, until thearrival rate without the discarded packets falls below the activationrate threshold and the process proceeds to step 318. In step 318, thesecond plurality of packets that are not discarded are processed andallowed to reactivate one or more mobile stations in a dormant state.The process then ends for this invocation and enters the next timeinterval where the process may be repeated.

Although the embodiment depicted in FIG. 3 illustrates the recalculationof the arrival rate after discarded each IP source group, this is notlimiting of the invention. Selective reactivation algorithm may evaluatewhich of the plurality of source IP groups should be discarded to bringthe arrival rate below the activation rate threshold and then discardthe one or more plurality of source IP groups all at once.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments; however, it will beappreciated that various modifications and changes may be made withoutdeparting from the scope of the present invention as set forth in theclaims below. The specification and figures are to be regarded in anillustrative manner, rather than a restrictive one and all suchmodifications are intended to be included within the scope of thepresent invention. Accordingly, the scope of the invention should bedetermined by the claims appended hereto and their legal equivalentsrather than by merely the examples described above.

For example, the steps recited in any method or process claims may beexecuted in any order and are not limited to the specific orderpresented in the claims. Additionally, the components and/or elementsrecited in any apparatus claims may be assembled or otherwiseoperationally configured in a variety of permutations to producesubstantially the same result as the present invention and areaccordingly not limited to the specific configuration recited in theclaims.

Benefits, other advantages and solutions to problems have been describedabove with regard to particular embodiments; however, any benefit,advantage, solution to problem or any element that may cause anyparticular benefit, advantage or solution to occur or to become morepronounced are not to be construed as critical, required or essentialfeatures or components of any or all the claims.

As used herein, the terms “comprise”, “comprises”, “comprising”,“having”, “including”, “includes” or any variation thereof, are intendedto reference a non-exclusive inclusion, such that a process, method,article, composition or apparatus that comprises a list of elements doesnot include only those elements recited, but may also include otherelements not expressly listed or inherent to such process, method,article, composition or apparatus. Other combinations and/ormodifications of the above-described structures, arrangements,applications, proportions, elements, materials or components used in thepractice of the present invention, in addition to those not specificallyrecited, may be varied or otherwise particularly adapted to specificenvironments, manufacturing specifications, design parameters or otheroperating requirements without departing from the general principles ofthe same.

1. A method of selective dormant data session reactivation in a radioaccess network, comprising: calculating an activation rate threshold asa function of a first plurality of packets received over a first timeinterval, wherein the first plurality of packets are coupled toreactivate at least one dormant mobile station and wherein the firstplurality of packets are received by a packet control function thatcommunicates the plurality of packets between the at least one dormantmobile station and a Packet Data Serving Node; buffering by the packetcontrol function a second plurality of packets received in a second timeinterval, wherein each of the second plurality of packets has adestination IP address coupled to reactivate the at least one dormantmobile station; comparing by the packet control function an arrival rateof the second plurality of packets in the second time interval to theactivation rate threshold; if the arrival rate exceeds the activationrate threshold, the packet control function: separating the secondplurality of packets into a plurality of source IP groups according totheir respective source IP addresses; discarding a one of the pluralityof source IP groups having a highest number of the second plurality ofpackets; iteratively performing the following steps until arrival rateis below the activation rate threshold: comparing the arrival rate ofthe second plurality of packets in the second time interval without theone of the plurality of source IP groups, to the activation ratethreshold; and if the arrival rate of the second plurality of packets inthe second time interval without the one of the plurality of source IPgroups exceeds the activation rate threshold, discarding a one of theplurality of source IP groups having a next highest number of the secondplurality of packets.
 2. The method of claim 1, further comprisingduring a third time interval, the packet control function processing thesecond plurality of packets not discarded, wherein the third timeinterval follows the first and second time intervals.
 3. The method ofclaim 1, wherein the second time interval follows the first timeinterval.
 4. The method of claim 3, wherein the first time interval islonger than the second time interval.
 5. The method of claim 1, whereinthe second time interval is a portion of the first time interval.
 6. Themethod of claim 1, wherein the activation rate threshold is a multipleof the first plurality of packets received over the first time interval.7. The method of claim 1, wherein discarding one of the plurality ofsource IP groups comprises preventing the plurality of second packets inthe one of the plurality of source IP groups from reactivating thedormant mobile station.
 8. The method of claim 1, further comprisingdefining at least one protected sender, wherein any of the secondplurality of packets received from the at least one protected sender areprevented from being discarded.